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Difficulty: HardNetworking Ports and Protocols

A tier-2 help desk technician is troubleshooting an issue on a legacy Windows workstation where local network shares can be accessed via IP address, but name resolution fails when attempting to register and locate computer names on the local broadcast domain without a DNS server. The technician suspects that NetBIOS Name Service traffic is being blocked by a host-based firewall rule. Which port and transport protocol combination must be permitted through the firewall to restore NetBIOS Name Service functionality?

  1. UDP port 137Answer
  2. B
    TCP port 139
  3. C
    UDP port 53
  4. D
    TCP port 445

Answer

UDP port 137 is required for NetBIOS Name Service name registration and resolution.
NetBIOS Name Service (NBNS) uses UDP port 137 to perform name registration, resolution, and release actions across local network segments when DNS is unavailable or not utilized.

Step-by-Step Solution

1
Identify the required network service from the scenario
The workstation requires NetBIOS Name Service (NBNS) to perform local host name resolution without DNS.
The stem specifies that name resolution fails when registering and locating computer names using NetBIOS broadcast methods.
2
Match NetBIOS sub-services to their corresponding ports and transport protocols
NetBIOS Name Service uses UDP 137, NetBIOS Datagram Service uses UDP 138, and NetBIOS Session Service uses TCP 139.
Name queries and broadcasts are connectionless operations requiring UDP transport over port 137.
3
Differentiate NetBIOS Name Service from NetBIOS Session Service and SMB
UDP 137 handles name resolution, TCP 139 handles NetBIOS file sessions, TCP 445 handles direct SMB, and UDP 53 handles standard DNS.
Selecting UDP 137 specifically addresses the name resolution filtering failure described.

Key Concept

NetBIOS Port Assignments
Estimated Time:1m 30s
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Topics

Networking Ports and Protocols

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